题解 | #找出字符串中第一个只出现一次的字符#

using namespace std;
int main()
{
    string s;
    getline(cin, s);
    bool flag = false;
    unordered_map<int, int> frequency;
        for (char ch: s) 
        {
            ++frequency[ch];
        }
        for (int i = 0; i < s.size(); ++i) 
        {
            if (frequency[s[i]] == 1) 
            {
                cout << s[i] << endl;
                flag = true;
                break;
            }
        }
    if(!flag)
    {
           cout << "-1" << endl;
    }
    return 0;
}